JPS5858344B2 - Process for treating cyanide by-products in nitrile production - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to 2) a method for producing IJ, particularly 2) a method for treating cyanide by-product acid produced during the production of IJ.

In producing nitrile by an ammoxidation process involving a reaction between an organic compound, ammonia and oxygen (directly or provided by an oxidized catalyst), small amounts of hydrogen cyanide and/or cyanogen are produced as by-products. Ammonium chloride is produced.

Such cyanides are highly toxic substances that cannot be released into the atmosphere; as a result, methods are needed to treat such cyanide byproducts to prevent their release into the atmosphere.

The present invention was pursued in an effort to provide a method for treating cyanide by-products generated in nitrile production.

According to one aspect of the invention, in an IJJ production process, wherein the nitrile product effluent contains gaseous ammonia, carbon dioxide and hydrogen cyanide, the process comprises:
An aqueous stream containing ammonium carbonate and ammonium cyanide, as well as hydrogen cyanide and at least some ammonia and carbon dioxide as an aqueous solution, is recovered from the nitrile product effluent, and the cyanide in the aqueous stream is hydrolyzed to form ammonia and carbon dioxide. A method is provided for recovering carbon oxide, and following hydrolysis, cyanide-free carbon monoxide, carbon dioxide, and ammonia, and also cyanide-free water.

According to another aspect of the invention, 2) a process for producing a nitrile in which the IJ product effluent contains gaseous ammonia carbon dioxide and hydrogen cyanide, wherein the process comprises: (a) containing ammonium carbonate and ammonium cyanide; b) hydrolyzing the cyanide present in said aqueous stream to ammonia and carbon monoxide; e) removing carbon monoxide, carbon dioxide, water vapor and unhydrolyzed hydrogen cyanide from the aqueous solution produced in step (b)) recovering cyanide-free water and stripped gas by IJ stripping; The stripped gas is converted into a gas stream of ammonia and carbon monoxide,
and (e) stripping the hydrogen cyanide-free carbon dioxide from the aqueous solution from step (d); (f) the aqueous solution from step Qe); passing at least a portion of the sample to step (b).

According to yet another aspect of the invention, 2) a process for producing nitriles in which the IJJ effluent comprises gaseous ammonia, carbon dioxide and hydrogen cyanide, wherein said process comprises (a) ammonium carbonate and ammonium cyanide; (b) stripping the aqueous solution of step (a) of carbon dioxide, water vapor and hydrogen cyanide; (e) separating the stripped gas into a gaseous stream of ammonia and an aqueous solution containing ammonium carbonate and ammonium cyanide; (d) step (e) (e) stripping the aqueous solution from step (d) of cyanide-free carbon dioxide and carbon monoxide; (f) passing at least a portion of the aqueous solution from step (e) to step b).

It will be appreciated that the present invention makes it possible to recover ammonium values from cyanide by-products.

In a preferred embodiment of the invention, the hydrolysis of cyanide present in the aqueous ammonium carbonate/ammonium cyanide solution is generally carried out at temperatures between 100 and 400'F, thereby converting ammonium cyanide to ammonia and carbon monoxide. .

Hydrolysis is generally carried out at naturally occurring pressures within the apparatus, however higher pressures could also be used.

Contacting is carried out at the hydrolysis temperature to achieve the desired single flow conversion of cyanide (
per pass conversion).

By circulating as described below, cyanide 100
1% total conversion of cyanide can be achieved.
It is not necessary to achieve 0.00% single flow conversion.

In one embodiment of the invention, an aqueous stream of ammonium carbonate and ammonium cyanide recovered from the nitrile production effluent is subjected to hydrolysis conditions to convert hydrogen cancer to ammonia and carbon monoxide.

The hydrolysis product is introduced into a stripping zone to strip the solution of volatiles, thereby obtaining a liquid product of substantially pure water free of cyanide.

The stripped gas mixture containing water vapor, ammonia, carbon monoxide, carbon dioxide and unconverted hydrogen cyanide is then introduced into an ammonia recovery zone from which ammonia recovery takes place.

In particular, the ammonia is recovered in a stripper absorber, in which the gaseous mixture is contacted with ammonia-enriched ammonium carbonate to produce an ammonia gas stream containing the carbon monoxide produced during hydrolysis, and a carbon dioxide-enriched carbon dioxide stream. Make an ammonium solution, and any unconverted ammonium cyanide present.

The solution is then introduced into a stripper to strip the carbon dioxide therefrom, creating an ammonia-enriched ammonium carbonate solution.

Some of the ammonium carbonate solutions containing a lot of ammonia are
Return to hydrolysis to effect hydrolysis of residual unconverted hydrogen cyanide present in the feed to the hydrogen cyanide recovery operation.

The remaining ammonia-rich ammonium carbonate solution portion is recycled to a stripper absorber for ammonia recovery.

The recovered ammonia may be recycled for nitrile production, and the carbon monoxide present in the ammonia is finally discharged from the device.

17) In an embodiment, the aqueous solution of ammonium carbonate and ammonium cyanide recovered from the nitrile production effluent is stripped of volatiles to produce a liquid stream of substantially pure water free of cyanide. and produce a gaseous mixture of water vapor, ammonia, carbon dioxide and hydrogen cyanide.

The gaseous mixture is then introduced into an ammonia recovery device (preferably a stripper absorber).

Here, cyanide-free ammonia is recovered from the gaseous mixture using an ammonia-enriched ammonium carbonate absorption solution.

Ammonia is recovered from the stripper absorber as a gas stream which is recycled to the nitrile production.

The liquid stream, which is a carbon dioxide-rich ammonium carbonate solution containing ammonium cyanide, then undergoes hydrolysis to convert the cyanide in the solution to ammonia and carbon monoxide.

The hydrolysis effluent is then introduced into a stripper to strip the cyanide-free carbon dioxide and carbon monoxide from the solution, creating an ammonia-enriched ammonium carbonate solution.

The ammonia-rich ammonium carbonate solution recovered from carbon dioxide and carbon monoxide stripping is used in a stripper absorber to recover ammonia.

Aqueous solutions of ammonium carbonate and ammonium cyanide are recovered from the nitrile product effluent generated in processes for producing aromatic, aliphatic or heterocyclic nitriles.

Representative examples of such diyl-IJ groups include aromatic nitriles containing one or more cyano groups, preferably one or two cyano groups, which may also be substituted with other substituents, such as alkyl groups. (can be replaced or not)
For example, phthalonitrile, terephthalonitrile, isophthalonitrile, tolnitrile, ■-cyanonaphthalene, 2
- 6-dicyatunaphthalene, etc.; or heterocyclic nitriles containing one or more cyano groups (generally the heterocyclic nucleus is pyridine), such as nicotinonitrile; or aliphatic nitriles, such as acrylonitrile, methacrylonitrile, etc. can be mentioned.

Such nitriles are generally made by the ammoxidation process.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more easily understood and, therefore, its advantages may be better appreciated, the invention will now be described by way of example with reference to the drawings.

Referring to FIG. 1, there is schematically shown an IJ production reaction zone, indicated generally at 10, which is supplied with a suitable feedstock by line 11.

The feed in line 11 contains the organic material to be converted to nitrile and ammonia, and also oxygen if the required amount of oxygen is to be provided by gaseous oxygen.

Alternatively, the amount of oxygen required for the process, as described above, may be provided by the use of a suitable catalyst material, such as oxidized vanadia on a suitable support.

Nitrile production reaction effluent is removed from reaction zone 10 by line 12; such effluent generally includes unreacted feedstock, nitrile product, organic intermediates, organic width products, water vapor, ammonia, carbon dioxide, and hydrogen cyanide. , such effluent is introduced into collection zone 13.

In recovery zone 13, the nitrile product is recovered via line 14, the ammonia-containing recycle stream via line 15, and the organic recycle stream via line 16.

Recovery zone 13 also recovers an aqueous stream containing ammonium carbonate and ammonium cyanide via line 17.

The operation of such recovery zones is known to those skilled in the art and does not form a novel part of the invention and will therefore not be described in detail.

Generally in recovery zone 13, the nitrile product effluent is contacted with a suitable quench liquid to recover a liquid stream containing the nitrile product and a gaseous stream containing organic matter as well as water vapor, carbon dioxide, ammonia and hydrogen cyanide. .

The residual gas stream is then further cooled to separate organic condensate, aqueous condensate (which contains ammonium carbonate and ammonium cyanide), and a gaseous recycle stream containing residual ammonia.

The aqueous stream of ammonium carbonate and ammonium cyanide in line 17 is obtained in line 1 as described below.
Combine it with the circulation flow in 8.

The combined streams in line 19 are introduced into hydrolyzer 21.

In the hydrolyzer 21, hydrogen cyanide is about ioO to about 40
At a temperature of 0'F, it is hydrolyzed at or above the natural pressure of the equipment to produce ammonia and carbon monoxide.

It is generally not possible to carry out complete hydrolysis of the hydrogen cyanide in the hydrolyzer 21, so that the hydrolysis effluent still contains ammonium cyanide.

The liquid hydrolysis effluent containing dissolved ammonium carbonate and a reduced amount of ammonium cyanide is removed from the hydrolyzer 21 by line 22 and the resulting ammonia-enriched ammonium carbonate in line 24 as described below. It is introduced into the solution stripper 23 together with the solution.

Stripper 23 operates under conditions to strip the aqueous solution of all volatile materials, resulting in liquid product and substantially pure water free of cyanide.

Generally, the stripper is used at a temperature of 150 to 250'F.
Operates at a pressure of 2 atmospheres.

However, it should be understood that the scope of the invention is not limited to such conditions.

Substantially pure, cyanide-free water is removed from stripper 23 by line 25, a first portion of which is passed through line 26 for use as described below.

The remainder of the water is discarded via line 27.

A gaseous overhead stream containing ammonia, carbon dioxide, carbon monoxide, hydrogen cyanide and water vapor is removed from the stripper 23 by line 28 and an ammonia recovery zone 29 in the form of a stripper absorber.
to be introduced.

The stripper absorber 29 operates to recover a cyanide-free ammonia and carbon monoxide gas stream and an aqueous liquid stream of carbon dioxide rich ammonium carbonate solution containing ammonium cyanide.

The stripper 29 is supplied with an ammonia-rich ammonium carbonate solution obtained as described below through a line 31.

Generally the stripper absorber 29 is about 120~2
It operates at temperatures on the order of 0.000''F and pressures on the order of about 1 to about 2 atmospheres.

Gaseous ammonia recovered from the stripper absorber 29 is transferred via line 32 to the nitrile producing reactor 10.
The carbon monoxide contained therein is eventually discharged from the device.

A carbon dioxide-rich aqueous solution of ammonium carbonate and unconverted ammonium cyanide is removed from stripper absorber 29 by line 33 and passed to stripper absorber 34 to strip the carbon dioxide from the solution.
Introduce it inside.

The ammonium cyanide concentration in the solution is low enough that cyanide is not stripped from the solution.

The stripper 34 is also supplied with water by line 26 to remove ammonia from the steam generated in the stripper 34.

Stripper 34 typically operates at a temperature of 200-400'F and a pressure of 5-20 atmospheres.

However, it should be understood that such conditions are illustrative and the scope of the present invention is not limited thereby.

Cyanide-free carbon dioxide is removed from stopper 34 by line 35; since such gas stream in line 35 is cyanide-free, such stream may be discharged directly to the atmosphere.

An ammonia-rich aqueous ammonium carbonate solution containing some ammonium cyanide is recovered from stripper 34 by line 36.

A first portion of this stream is used in line 31 to absorb carbon dioxide introduced into the stripper absorber by line 28.

Another part thereof is connected to the solution stripper 2 by line 24.
Introduced in 3.

Another portion thereof is recycled through line 18 to hydrolyzer 21 for hydrolysis of residual cyanide as described above.

By recycling a portion of the C bottoms from the carbon dioxide stripper 34, substantially complete hydrolysis of the cyanide present in the aqueous stream in line 17 is obtained.

Another embodiment of the invention is shown in FIG.

Referring to FIG. 2, line 101 is obtained from the nitrile product effluent, as described above with respect to the embodiment of FIG.
The aqueous solution of ammonium carbonate and ammonium cyanide therein is introduced into solution stripper 102 along with an ammonia-rich ammonium carbonate solution in line 103 obtained as described below.

The stripper 102 operates under conditions to strip all volatile materials from the aqueous solution, and the solution stripper 23
Create substantially pure water free of cyanide as described above.

Substantially pure water free of cyanide is provided in line 104.
The first portion is then passed through line 105 for use as described below.

The remaining water is discarded in line 106.

A gaseous overhead stream of ammonia, carbon dioxide, hydrogen cyanide and water vapor is removed from the stripper 102 by line 107 and transferred to the stripper absorber.
29 into a stripper absorber 108 which is operated as described above for 29.

Stripper 108 is supplied with an ammonia-enriched ammonium carbonate solution via line 109.

Cyanide-free ammonia overhead can be removed from the stripper oven 108 by line 111 and recycled to the nitrile production reactor.

A carbon dioxide rich aqueous solution of ammonium carbonate and ammonium cyanide is removed from the stripper absorber 108 by line 112 and introduced into a hydrolyzer 113 where the ammonium cyanide is hydrolyzed to ammonia as described above. Turn into carbon monoxide.

The hydrolysis effluent is transferred to the hydrolysis unit 11 by line 114.
Remove carbon monoxide and carbon dioxide from Step 3)
It is introduced into the stripper 115 for IJ stripping.

The stripper 115 is also supplied with water by line 105 for scavenging ammonia from the vapor generated in the stripper.

Cyanide-free gaseous carbon oxides and carbon dioxide may be removed from the stripper 115 by line 116 and vented directly to the atmosphere.

Ammonium carbonate solution containing a lot of ammonia is line 1
17 from the stripper 115, the first part of which is passed through line 109 for introduction into the IJ collar absorber 108.

Another portion thereof is passed through line 103 and introduced into solution stripper 102.

The present invention will be further explained by examples.

Example 1 The present invention demonstrates the ability to hydrolyze cyanide in aqueous solution according to the example of FIG.

The test was carried out on an outer diameter 1 with a thermometer protection tube down the length of the reactor.
The experiment was carried out in an apparatus such as that shown in FIG. 1 containing a continuous vertical hydrolysis reactor made from 316 stainless steel with a height of 13 inches.

The liquid was poured upward. The lower 3-4 inches of the reactor served as a preheater.

The total liquid holding capacity of the reactor is 135+-...5
It was CC.

Overflow was collected in a cold ejector.

The equipment pressure is 50 to 100 ps higher than the normal steam pressure during operation.
I kept the ig high.

Cyanide concentration was measured using the pot temperature method.

Ammonia and carbon dioxide contents were determined by acid titration.

Operating conditions and results are shown in Table I.

Example 2 This example demonstrates the ability to hydrolyze cyanide in aqueous solution by way of the example of FIG.

The test was conducted in a 155 cc batch 316 stainless steel reactor.

The operating conditions and results are shown in Table ■. In a preferred embodiment of the invention, without releasing cyanide into the atmosphere,
2) It has been found to be particularly advantageous that it is possible to remove the hydrogen cyanide by-product produced in the IJ production step.

Furthermore, the ammonia present in the cyanide can be effectively recovered for use throughout the process.

In the embodiment shown in FIG. 1, hydrolyzing the cyanide prior to the recovery operation also reduces the tendency to form polymers from cyanide, ammonia, and carbon dioxide that result in solid deposits.

In the embodiment of FIG. 2, reduced energy and capital costs (hydrolysis and CO2 recovery are carried out under similar conditions) are obtained at the risk of increased solids deposition.

[Brief explanation of drawings]

FIG. 1 is a simplified process diagram of one embodiment of the invention, and FIG. 2 is a simplified process diagram of another embodiment of the invention. 10 is 2) IJ production reaction zone, 13 is recovery zone, 2
1 is a hydrolyzer, 23 is a solution stripper, 29 is an ammonia recovery zone (stripper/absorber), 34
, 102 is a stripper, 108 is a stripper/absorber, 113 is a hydrolyzer, and 115 is a stripper.

Claims (1)

Claims: 1. A process for producing nitriles in which the nitrile product effluent contains gaseous ammonia, carbon dioxide, and hydrogen cyanide, comprising: (a) an aqueous stream containing ammonium carbonate and ammonium cyanide; recovering hydrogen cyanide in solution and at least a portion of ammonia and carbon dioxide from the nitrile production effluent; (b) hydrolyzing the cyanide present in the aqueous stream to ammonia and carbon monoxide; (e) step stripping carbon monoxide, carbon dioxide, water vapor and unhydrolyzed hydrogen cyanide from the aqueous solution produced in (b) to recover cyanide-free water and stripped gas; , a gaseous stream of ammonia and carbon monoxide, and an aqueous solution containing ammonium carbonate and ammonium cyanide; e) stripping the hydrogen cyanide-free carbon dioxide from the aqueous solution from step (d);
) A process for the production of nitrile, characterized in that at least a part of the aqueous solution from e) is passed through step (b). 2. The method according to claim 1, wherein the hydrolysis is carried out at a temperature of 100 to 400°C. 3. Process according to claim 1 or 2, in which the stripped ammonia and carbon monoxide are recycled to the nitrile production. 4. A method according to any one of claims 1 to 3, wherein the stripping in step (e) is carried out at a temperature of 150 to 250°C and a pressure of 1 to 2 atmospheres. 5. Stripping in step (e) at 200~400″F
5. A method according to any one of claims 1 to 4, which is carried out at a temperature of from 5 to 20 atmospheres. 6. A method according to any one of claims 1 to 4, wherein a portion of the aqueous solution from step (e) is recycled to step (d). 7. A method according to any one of claims 1 to 6, in which a portion of the water recovered in step (e) is passed through step (me). 8 Step (d) at a temperature of 120-200'F and 1-
8. The method according to claim 1, wherein the method is carried out at a pressure of 2 atmospheres.